What is the purpose of swinging the hand signal for Apply Air Brakes horizontally above the head?

Swinging the hand signal for Apply Air Brakes horizontally above the head serves a specific and critical function in train operations. This gesture is a clear and universal signal intended to communicate with the train crew on duty. By utilizing this hand signal, the conductor or operator is able to effectively convey the command to apply the air brakes, which is essential for ensuring the safety of the train's operation, particularly in managing speed and stopping when necessary.

This signaling method is designed to be easily recognized by crew members from a distance or in situations where voice communication might not be feasible due to noise or other conditions. Proper signaling is crucial in maintaining coordination among crew members, which ultimately enhances the safety and efficiency of train movements.

In contrast, the other options do not accurately reflect the role of this specific hand signal in the context of train operations. For example, while signaling for speed reduction is important, it is not the primary function of the horizontal hand signal for applying air brakes. Communication with maintenance crews or alerting other trains may require different signals or methods of communication that are more suited to those contexts.